Plasma-assisted processing system and plasma-assisted processing method

ABSTRACT

A plasma-assisted processing system has a lifting mechanism capable of vertically moving a microwave power unit and a waveguide to adjust the level of a planar slot antenna disposed on an expanded lower end part of the waveguide. A space extending under the antenna is surrounded by a shielding member. An optical sensor having an array of photosensors is disposed on the outer side of a window formed in the side wall of a vacuum vessel to monitor the lower limit level of a cease region for a plasma (cease level). An ideal distance between the cease level and the antenna is determined beforehand and the level of the antenna is adjusted on the basis of a measured cease level so that the antenna is spaced the ideal distance apart from the cease level. Since the difference between the cease level and a level X 0  for the cutoff density of an X-wave is fixed, the level X 0  may be monitored instead of the cease level.

This is a divisional of application Ser. No. 09/595,476, filed Jun. 16,2000 now U.S. Pat. No. 6,528,752, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plasma-assisted processing system anda plasma-assisted processing method that produce a plasma by using theenergy of a high-frequency wave, such as a microwave, and use the plasmafor processing a substrate, such as a semiconductor wafer.

2. Description of the Related Art

A semiconductor device manufacturing process includes a step ofprocessing a semiconductor wafer (hereinafter referred to simply as“wafer”) by using a plasma FIG. 16 shows a known microwaveplasma-assisted processing system that carries out a plasma-assistedprocess. As shown in FIG. 16, the microwave plasma-assisted processingsystem has a vacuum vessel 9 provided with a stage 91 for supporting awafer W thereon, a planar slot antenna 92 disposed in a ceiling regionof the vacuum vessel 9, a microwave power unit 93, a coaxial waveguide94 provided with a shaft 94 a and connected to the microwave source 93and the vacuum vessel 9, a microwave transmitting plate 95 of quartz,and a gas supply unit 96. A microwave generated by the microwave powerunit 93 is guided through the waveguide 94, the antenna 92 and themicrowave transmitting plate 95 into the vacuum vessel 9, a process gassupplied by the gas supply unit 96 into the vacuum vessel 9 is ionizedby the microwave to produce a plasma, and the plasma is used for forminga film on the wafer W or for etching a film formed on the wafer W.

A plasma is a complicated combination of electrical, physical andchemical phenomena and its mechanism has many points which have not yetbeen elucidated. As matters stand, the dependence of the condition of aplasma on process conditions has not been definitely elucidated.Therefore, even if a highly uniform plasma can be produced under certainprocess conditions including pressure and power of a microwave,sometimes, the uniformity of the plasma is deteriorated under otherprocess conditions.

The uniformity of a plasma is reflected directly on the uniformity of afilm thickness or the uniformity of etch rate. Since the recentsemiconductor devices are miniaturized and are provided with thin films,the yield of semiconductor devices is greatly dependent on theuniformity of the plasma. Accordingly, the development of techniquescapable of producing a highly uniform plasma regardless of processconditions has been desired.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a plasma-assistedprocessing system and a plasma-assisted processing method capable ofproducing a highly uniform plasma and of processing a substrate in ahigh intrasurface uniformity.

According to a first aspect of the present invention, a plasma-assistedprocessing system comprising a vacuum vessel internally provided with astage, a high-frequency wave transmitting plate attached to the vacuumvessel, a planar antenna disposed opposite to the high-frequency wavetransmitting plate, and a high-frequency power unit that sends ahigh-frequency wave for producing a plasma to the antenna, and capableof propagating a high-frequency wave for producing a plasma through theantenna and the high-frequency wave transmitting plate into the vacuumvessel, of producing a plasma by ionizing a processing gas supplied intothe vacuum vessel by the energy of the high-frequency wave and ofprocessing a substrate mounted on the stage in the vacuum vessel byusing the plasma; comprises: a lifting mechanism that moves the antennavertically relative to the vacuum vessel; an electromagnetic shieldingmember surrounding a region between the antenna and the high-frequencywave transmitting plate; a level estimating unit that estimates a levelof high-frequency wave cutoff density formed between the high-frequencywave transmitting plate and a plasma producing region; and a controllerthat controls the lifting mechanism to adjust the level of the antennaso that a cavity of a proper size for the high-frequency wave is formedbetween the antenna and the level of a cutoff density for thehigh-frequency wave for producing a plasma.

Since the lower end of the cavity for the high-frequency wave can beknown, the level of the antenna can be properly adjusted on the basis ofthe result of operation of the level estimating unit by determining theproper size of the cavity beforehand.

According to a second aspect of the present invention, the levelestimating unit includes a transparent plate covering an opening formedin a side wall of the vacuum vessel, and a cease region detecting unitcapable of optically detecting a lower limit level of a cease region inwhich a plasma produced in the plasma producing region ceases betweenthe high-frequency wave transmitting plate and a region in which theplasma is luminescent, and the level of the cutoff density is estimatedon the basis of the detected lower limit level for the cease region.

According to a third aspect of the present invention, the levelestimating unit includes a high-frequency wave radiating unit thatdelivers a detecting high-frequency wave from above the plasma to theplasma, and a high-frequency wave receiving unit that receives thedetecting high-frequency wave delivered to and reflected by the plasma,a level of the cutoff density for the detecting high-frequency wave isdetermined on the basis of a position of the reflected high-frequencywave on the high-frequency wave receiving unit, and a level of thecutoff density for the plasma producing high-frequency wave is estimatedon the basis of the level of the cutoff density for the detectinghigh-frequency wave.

Although the level of a cutoff density for the plasma producinghigh-frequency wave and the lower limit level of the cease region aredifferent from each other, the difference between those levels can beregarded as substantially fixed. Therefore, those results of detectioncan be used in substitution for the level of a cutoff density for theplasma producing high-frequency wave. Estimation of the level of acutoff density for the high-frequency wave includes the use of thedetected lower limit level of the cease region of the plasma and thedetected level of a cutoff density for the detecting high-frequency waveas substitutes, and includes the estimation of the level of a cutoffdensity for the plasma producing high-frequency wave on the basis of apredetermined algorithm.

According to a fourth aspect of the present invention, a plasma-assistedprocessing system comprising a vacuum vessel internally provided with astage, a high-frequency wave transmitting plate attached to the vacuumvessel, a planar antenna disposed opposite to the high-frequency wavetransmitting plate, and a high-frequency power unit that delivers ahigh-frequency wave for producing a plasma to the antenna, and capableof propagating a high-frequency wave for producing a plasma through theantenna and the high-frequency wave transmitting plate into the vacuumvessel, of producing a plasma by ionizing a processing gas supplied intothe vacuum vessel by the energy of the high-frequency wave and ofprocessing a substrate mounted on the stage in the vacuum vessel byusing the plasma; comprises: a lifting mechanism that moves the antennavertically relative to the vacuum vessel; an electromagnetic shieldingmember surrounding a region between the antenna and the high-frequencywave transmitting plate; a storage unit that stores set antenna levelsfor recipes for plasma-assisted process; and a controller that reads alevel of the antenna for a selected recipe from the storage unit andcontrols the lifting mechanism to adjust the level of the antenna.

According to a fifth aspect of the present invention a plasma-assistedprocessing method comprises the steps of: propagating a plasma producinghigh-frequency wave delivered by a high-frequency power unit through aplanar antenna and a high-frequency wave transmitting plate into avacuum vessel; producing a plasma by ionizing a processing gas suppliedinto the vacuum vessel by the energy of the high-frequency wave; andprocessing a substrate supported on a stage disposed in the vacuumvessel; wherein the substrate is processed by a plasma-assisted processafter adjusting the level of the antenna relative to the vacuum vesselso that a cavity region of a proper size for the high-frequency wave isformed between the antenna and a level of a cutoff density for thehigh-frequency wave in the vacuum vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are views of assistance in explaining results ofobservation of a plasma;

FIG. 2 is a graph showing an ion current intensity distribution in aplasma;

FIG. 3 is a typical view of a cavity for a microwave;

FIG. 4 is a graph showing the variation of electron density with theposition of a microwave in a vacuum vessel relative to a microwavetransmitting plate;

FIG. 5 is a typical view of assistance in explaining the reflection of amicrowave at a position of a cutoff density for an X-wave;

FIG. 6 is a table of assistance in explaining the relation betweenprocess conditions and position of a cutoff density for an X-wave;

FIG. 7 is a schematic longitudinal sectional view of a plasma-assistedprocessing system in a first embodiment according to the presentinvention;

FIG. 8 is an enlarged sectional view of a portion of the plasma-assistedprocessing system shown in FIG. 7;

FIG. 9 is view of assistance in explaining a cavity for a microwavebefore and after the adjustment of the level of an antenna;

FIGS. 10, 11 and 12 are graphs showing electron density distributions ina processing vessel under different conditions;

FIG. 13 is a block diagram of a control system included in aplasma-assisted processing system in a second embodiment according tothe present invention;

FIG. 14 is a typical view of assistance in explaining the resonance ofelectric field intensity distributions respectively over and under amicrowave transmitting plate;

FIGS. 15A and 15B are views of assistance in explaining the shape of across section of a wall between an upper part of a microwavetransmitting plate and a vacuum chamber; and

FIG. 16 is a schematic longitudinal sectional view of a conventionalplasma-assisted processing system.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Matters on the basis of which plasma-assisted processing systemsaccording to the present invention have been designed will be describedprior to the description of plasma-assisted processing systems embodyingthe present invention. A plasma produced in the vacuum vessel 9 includedin the conventional plasma-assisted processing system shown in FIG. 16was observed by using a CCD camera embedded in the stage 91 disposed inthe vacuum vessel 9 and having an upper part formed of quartz. Argon gaswas supplied from the gas supply unit 96 into the vacuum vessel 9 and a2.45 GHz microwave was propagated from the microwave power unit 93 intothe vacuum vessel 9 to produce a plasma by ionizing the argon gas. Thepower of the microwave and the pressure in the vacuum vessel 9 werevaried and the condition of the plasma was observed. The brightness ofthe plasma was uniform under some conditions and was irregular underother conditions.

FIGS. 1A and 1B are views showing images of plasmas taken by the CCDcamera. FIG. 1A shows an irregular plasma having particularly brightregions and FIG. 1B shows a uniform plasma having uniform brightness.

Table 1 shows process conditions and the condition of plasmas.

TABLE 1 Pressure (mtorr) Microwave power (kW) Condition of plasma A 50 2Irregular brightness B 100 2 Uniform brightness C 50 5 Uniformbrightness

Ion current intensity distribution in the vacuum vessel 9 with respectto radial directions was measured under the foregoing processconditions. Measured results are shown in FIG. 2. Under the processcondition A, ion current intensity increases from a position on the wallof the vacuum vessel 9 toward the center of the same. Ion currentintensity distributions under the process conditions B and C aresubstantially the same; ion current intensity under the processconditions B and C is substantially on the same level between the wallof the vacuum vessel 9 and the center of the same. In FIG. 2, the ioncurrent intensity distributions under the process conditions B and C areindicated by a single curve for the sake of convenience.

Ion current intensity is dependent on the electron density of theplasma. The size of a plasma cease region, i.e., a region near the wallin which the plasma is not luminescent, is dependent on electrondensity. The inventors of the present invention noticed a fact that thesize of the plasma cease region is related with the size of a microwavecavity extending over the plasma. The cavity is formed between theantenna 92 and a position of a cutoff density for the microwave. In FIG.3 shaded region S is a cavity.

FIG. 4 is a graph showing the variation of electron density withdistance from the lower surface of the microwave transmitting plate 95in the vacuum vessel 9. A cutoff density X0 for the plasma producingmicrowave is at a position at a certain distance from the microwavetransmitting plate 95. As shown in FIG. 5, on the level of the cutoffdensity X0 (hereinafter referred to as “level X0”), the plasma producingmicrowave falling from above the level X0 is reflected. A portion of theplasma near the wall of the vacuum vessel 9 is in a cease region inwhich the plasma is not luminescent. The level X0 is below a level L0 ofthe lower limit of the cease region (hereinafter referred to as “ceaselevel L0”), and the difference between those levels is substantiallyconstant.

Since the microwave is reflected on the level X0, the level X0 can bedetermined, for example, by radiating an electromagnetic wave obliquelydownward toward, for example, a central region of the vacuum vessel 9 byan electromagnetic wave radiator 97 disposed on an electromagneticshielding member extending between the antenna 92 and the microwavetransmitting plate 95 as shown in FIG. 5, receiving the reflectedelectromagnetic wave by an electromagnetic wave receiver 98, andcalculating the level of a position from which the electromagnetic waveis reflected on the basis of a position at which the reflectedelectromagnetic wave falls on the electromagnetic wave receiver 98.

When a microwave of the same frequency as that of the plasma producingmicrowave is radiated by the electromagnetic wave radiator 97, theelectromagnetic wave receiver is unable to discriminate between themicrowave radiated by the electromagnetic wave radiator 97 and theplasma producing microwave radiated by the antenna 92. Therefore, ameasuring microwave of a frequency different from that of the plasmaproducing microwave is radiated by the electromagnetic wave radiator 97.The level of a cutoff density for the measuring microwave (hereinafterreferred to as “level X1”) can be determined. The relation between theLevels X0 and X1 is dependent on the frequency difference and could beexpressed by: X1=X0+α, where “=” signifies approximately equal. Since αis the difference between the levels X1 and X0, α can be regarded assubstantially constant, the detected level X1 can be used insubstitution for the level X0 without any problem. The frequency of themeasuring microwave is, for example, in the range of several gigahertzto about 30 GHz. The lower limit frequency, when considered inconnection with the shape of the vacuum chamber, is on the order ofseveral gigahertz. Since frequency is proportional to the square root ofcutoff density (electron density), the upper limit frequency is on theorder of 30 GHz at the highest. The electromagnetic wave receiver 98 maycomprise a plurality of wave receiving elements in a verticalarrangement and may estimate the position of the reflectedelectromagnetic wave on the basis of the position of the wave receivingelement that receives the electromagnetic wave or may comprise a singlewave receiving element that is moved vertically for scanning and mayestimate the position of the reflected electromagnetic wave from aposition where the scanning wave receiving element receives thereflected electromagnetic wave. Since the interval between the level X0and the cease level, the cease level may be detected optically and maybe used in substitution for the level X0.

The positions of the X0 under different process conditions weremeasured. Measured results are shown in FIG. 6, in which “Level X0”signifies distance from the lower surface of the microwave transmittingplate 95 to the level X0. As obvious from data shown in FIG. 6, thelevel X0 approaches the microwave transmitting plate 95 as the power ofthe microwave increases, and the level X0 approaches the microwavetransmitting plate 95 as the pressure increases.

Since the size of the cavity for the microwave and the condition of theplasma are thus dependent on the process conditions, the condition ofthe plasma is connected with the size of the cavity. Therefore, it isconsidered that a uniform plasma having uniform brightness can beproduced regardless of process conditions by properly regulating thesize of the cavity. More specifically, A cavity of a proper size isformed by determining a proper size of a cavity beforehand, detectingthe position of the level X0 when carrying out a process, and adjustingthe height of the antenna 92. Since the position of the level X0 changesscarcely when the height of the antenna 92 is changed under some processconditions, adjustment is made so that distance between the antenna 92and the level X0 coincides with the vertical length of the propercavity.

A plasma-assisted processing system according to the present inventionshown in FIG. 7 which will be described hereinafter is an embodiment ofthe foregoing techniques. Referring to FIG. 7, the plasma-assistedprocessing system has a vacuum vessel 1 of, for example, a cylindricalshape, and a stage 2 disposed in the vacuum vessel 1 to support a waferW, i.e., a substrate, thereon. A discharge pipe 11 through which thevacuum vessel 1 is evacuated is connected to the bottom wall of thevacuum vessel 1. An electrode 22 is embedded in the stage 2 and isconnected to a high-frequency bias power unit 21 to apply, for example,a 13.56 MHz bias voltage to the stage 2. The stage 2 is provided with atemperature adjusting unit, not shown, to adjust the temperature of thewafer W to a predetermined temperature. An open end of the vacuum vessel1 is covered with a microwave transmitting plate 23 of a dielectricmaterial, such as quartz. A planar antenna 32 provided with a pluralityof slots 31 is disposed opposite to the microwave transmitting plate 23.

A coaxial waveguide 33 has an inner pipe 33 a and an outer pipe 33 bcoaxially surrounding the inner pipe 33 a. One end of the inner pipe 33a of the coaxial waveguide 33 is connected to a central part of theantenna 32. A lower end part of the outer pipe 33 b is expanded radiallyand extended axially downward to form a flat, cylindrical part 34. Arectangular waveguide 35 has one end connected to the side surface ofone end of the coaxial waveguide 33 remote from the antenna 32, and theother end connected through an impedance matching unit, not shown, to amicrowave power unit 36. The microwave power unit 36 is held on aholding table 41 which can be vertically moved by a lifting mechanism 4.The microwave power unit 36 and the waveguides 33 and 35 can bevertically moved by the lifting mechanism 4. The lifting mechanism 4 maybe, for example, a motor-driven jack or a lifting device employing aball screw and a pneumatic cylinder actuator.

An electromagnetic shielding cylinder 42 of a metal is set up on aperipheral part of the microwave transmitting plate 23. An annular platespring 43 having a U-shaped cross section is fitted in an annular spacebetween the inner surface of the shielding cylinder 42 and the outersurface of the expanded part 34 of the waveguide 33. Since the waveguide33 can be vertically movable as mentioned above, the plate spring 43separates a space under the antenna 32 from a space around the waveguide33 and guides the expanded part 34.

The inner pipe 34 of the waveguide 33 is cylindrical. A gas supply pipe5 is extended through the inner pipe 34. As shown in FIG. 8, an opening24 is formed in a central part of the microwave transmitting plate 23and a metal ring 51 is fitted in the opening 24. The free end of the gassupply pipe 5 is welded to a flange formed on the metal ring 51. Atelescopic electromagnetic shielding device 52 is disposed below theinner pipe 33 a so as to surround the gas supply pipe 5. Theelectromagnetic shielding member 52 is formed by sequentially nesting aplurality of metal cylinders 52 a, 52 b and 52 c one in one another. Thegas supply pipe 5 is extended through the inner pipe 33 a so as to bemovable relative to the inner pipe 33 a and the outer pipe 33 b. Thus,the waveguide 33 can be moved vertically with the gas supply pipe 5fixed.

A transparent plate 61 of, for example, quartz is fitted in an openingformed in the side wall of the vacuum vessel 1 and a cease leveldetector 62 for detecting the cease level (the lower limit level of acease region) is disposed on the outer surface of the transparent plate61. The cease level detector 62 may be an light sensor array of aplurality of light sensors vertically arranged with their optical axesextended horizontally. The light sensors corresponding to regions inwhich the plasma is luminescent are on and those corresponding to acease region are off. Thus, a cease level can be detected by the ceaselevel detector 62. A controller 63 receives a detection signal from thecease level detector 62 and a level signal from the lifting mechanism 4.The controller 63 finds the level of the antenna 32 on the basis of apulse signal generated by an encoder connected to a motor included inthe lifting mechanism 4. The controller 63 calculates a distance bywhich the antenna 32 must be vertically moved on the basis of the levelof the antenna and the cease level and gives a control signal to thelifting mechanism 4 to move the antenna 32 by the calculated distance.

The operation of the plasma assisted processing system will bedescribed. The proper size of a cavity for the microwave for processinga wafer W by a plasma-assisted process, such as a plasma-assisted filmforming process for forming a polysilicon film on the wafer W, isdetermined beforehand.

As mentioned above, a cavity suitable for producing a plasma of uniformbrightness may be determined through the observation of the plasma usingthe CCD camera. The cavity of the proper size is stored in thecontroller 63. The size of the cavity extends, on definition, betweenthe antenna 32 and the level X0. Since the distance between the ceaselevel and the level X0 is substantially fixed, storage of the properdistance H between the antenna 32 and the cease level is substantiallyequivalent to storage of the size of the cavity when the height of theantenna 32 is controlled through the detection of the cease level.

When processing a wafer W following a recipe, i.e., a set of processconditions including pressure, microwave power and such, a plasma isproduced following the recipe and a cease level L0 is detected by thecease level detector 62 before actually processing the wafer W. Thecontroller 63 gives a control signal to the lifting mechanism 4 toadjust the level of the antenna 32 so that the distance between theantenna 32 and the cease level L0 is adjusted to the distance H. FIG. 9is a view of assistance in explaining the adjustment of the level of theantenna 32. If the height of a cavity, i.e., a region between theantenna 32 and the cease level L0, is H+h1, the height of the antenna 32is reduced by h1 (the level X0 remains unchanged) to reduce the heightof the cavity to H. As mentioned above, the level X1 of a cutoff densityfor the measuring microwave is detected by the same procedure, in whichthe distance between the antenna and the level X1 is H.

The cease level detector 62 and the controller 63 serve as a levelestimating unit that estimates the level X0. When the electromagneticwave radiator 97 and the electromagnetic wave receiver 98 shown in FIG.5 are used for detecting the level X1, the electromagnetic wave radiator97, the electromagnetic wave receiver 98 and the controller serve as alevel estimating unit that estimates the level X0. Estimation of thelevel X0 includes using the cease level L0 or the detected level X1 insubstitution for the level X0, and estimating the level X0 by using analgorithm on the basis of the cease level L0 or the detected level X1.

After the completion of the foregoing adjustment, a wafer W is carriedinto the vacuum vessel 1 and is mounted on the stage 2. Then, the vacuumvessel 1 is evacuated to a predetermined vacuum of, for example, 10⁻⁶torr and monosilane (SiH₄) gas, i.e., a film forming gas, and Ar gas,i.e., a carrier gas, are supplied into the vacuum vessel 1.Subsequently, the microwave power unit 36 delivers plasma producingmicrowave power of, for example, 2.45 GHz and 2.5 kW and the bias powerunit 21 applies bias power of, for example, 13.56 MHz and 1.5 kW to thestage 2.

The microwave generated by the microwave power unit 36 is guided forpropagation by the waveguides 35 and 33 to the expanded part 34 and ispropagated through the slots 31 of the antenna 32 into the vacuum vessel1. The microwave ionizes the monosilane gas to produce active species,and the active species are deposited on a surface of the wafer W to forma polysilicon film.

When using another recipe, the level of the antenna is adjusted by theforegoing procedure before processing wafers W. The proper size H of thecavity is measure beforehand by using a processing gas to be used, suchas monosilane gas. If the proper sizes of cavities for different gasesare similar, the measured size may be used as the proper size H.

Since a plasma is produced so as to conform to the cavity of the propersize even if the recipe is changed, the plasma can be produced in a highuniformity at all times and the substrate can be processed in a highintrasurface uniformity, for example, to form a film of a uniformthickness on the wafer.

FIGS. 10 to 12 show the results of experiments conducted by using theplasma-assisted processing system shown in FIG. 7 to examine the effectof the level of the antenna 32 on electron density. In the experimentsto obtain data shown in FIG. 10, Ar gas was supplied into the vacuumvessel 1 and the pressure in the vacuum vessel was adjusted to 30 mtorr(3.99 Pa), a plasma was produced by delivering 2.45 GHz, 2 kW microwavepower by the microwave power unit 36 and applying 13.56 MHz, 1.5 kW biaspower to the stage 2 by the bias power unit 21, and a region at 10.5 cmfrom the lower surface of the microwave transmitting plate 23 wasscanned along a diameter of the vacuum vessel 1 with a probe to measureelectron densities. In FIG. 10, distance from the side wall of thevacuum vessel 1 measured along the diameter of the vacuum vessel ismeasured on the horizontal axis and electron density is measured on thevertical axis. In FIG. 10, a point at 0.0 on the horizontal axiscorresponds to a position on the side wall of the vacuum vessel and apoint at 27.0 on the horizontal axis corresponds to the center of thevacuum vessel 1.

Experiments were conducted under conditions similar to those for theexperiments to obtain data shown in FIG. 10, except that the pressure inthe vacuum vessel 1 was adjusted to 50 mtorr (6.6 Pa) and date shown inFIG. 11 was obtained. As obvious from the comparative observation ofFIGS. 10 and 11, the plasma produced at 50 mtorr is inferior inuniformity to that produced at 30 mtorr. The level of the antenna 32 wasraised by 0.5 mm and similar experiments were conducted at 50 mtorr.Data shown in FIG. 12 was obtained. As obvious from FIG. 12, raising ofthe level of the antenna 32 was effective in improving the uniformity ofthe plasma.

The experimental results verified that the cease level rises, i.e., thecease level approaches the microwave transmitting plate 23, when the gaspressure is increased to increase the density of the plasma and hence auniform plasma can be produced by raising the level of the antenna 32 tosecure a proper distance between the antenna 32 and the plasma.

The vacuum vessel 1 may be moved vertically instead of moving theantenna 32. The plasma-assisted process may be an etching process or anashing process. An RF power unit or a UHF power unit may be used forionizing a processing gas instead of the microwave power unit. In thisspecification, microwave power units, RF power units and UHF power unitsare called inclusively high-frequency power units. A plasma may beproduced by ionizing a processing gas by the electron cyclotronresonance of a microwave and a magnetic field.

According to the present invention, as shown in FIG. 13, levels ofantenna 32 suitable for forming cavities of proper sizes for recipes maybe determined and stored in a storage unit 71 beforehand, a CPU 73 mayread a level of the antenna 32 for a recipe selected by a recipeselecting unit 72, a controller 74 may give a control signal to thelifting mechanism 4 to set the antenna 32 on the level read by the CPU73. The proper level of the antenna 32 may be determined on the basis ofthe previously determined proper size H of the cavity by detecting acease level for each recipe or may be determined by adjusting the levelof the antenna 32 for each recipe observing the condition of theprocess. The antenna 32 may be vertically moved by a metal bellowsextended between a peripheral part of the antenna 32 and a peripheralpart of the microwave transmitting plate 23.

There is the possibility that an electric field intensity distributionin the vacuum vessel 1 caused by a cavity surrounded by a wall part 40extending between the antenna 32 and the microwave transmitting plate 23and an electric field intensity distribution caused by a cavity in thevacuum vessel 1 are emphasized as shown in FIG. 14 when both a wall partcorresponding to the electromagnetic wave shielding member 42 and thevacuum vessel 1 are cylindrical. Therefore, the wall part 40 and theantenna 32 may be formed respectively in shapes having hexagonal crosssections and the vacuum vessel 1 may be formed in a cylindrical shapehaving a circular cross section, or the wall part 40 and the antenna 32may be formed respectively in cylindrical shapes and the vacuum vessel 1may be formed in a shape having a polygonal cross section as shown inFIG. 15A. Both the vacuum vessel 1 and the electromagnetic shieldingcylinder 42 may be formed respectively in shapes having n-sidedpolygonal cross sections (in FIG. 6, hexagonal cross sections) and maybe disposed with the corners thereof circumferentially dislocatedrelative to each other as shown in FIG. 15B. The vacuum vessel 1 and theelectromagnetic shielding cylinder 42 may be formed respectively inshapes having special curvilinear cross sections other than polygonalcross sections. When the wall part 40 and the vacuum vessel 1 are formedin shapes having different cross sections, respectively, the wall part40 and the vacuum vessel 1 have different microwave modes, respectively,whereby the emphasis of the electric field intensity distribution can bereduced or avoided and the uniformity of the plasma can be improved.

As apparent from the foregoing description, according to the presentinvention, a highly uniform plasma can be produced and a substrate canbe processed in a high intrasurface uniformity.

What is claimed is:
 1. A plasma-assisted processing system including avacuum vessel internally provided with a stage, a high-frequency wavetransmitting plate attached to the vacuum vessel, a planar antennadisposed opposite to the high-frequency wave transmitting plate, and ahigh-frequency power unit that delivers a high-frequency wave forproducing a plasma to the antenna, wherein the plasma-assistedprocessing system propagates a high-frequency wave for producing aplasma through the antenna and the high-frequency wave transmittingplate into the vacuum vessel, produces a plasma by ionizing a processinggas supplied into the vacuum vessel by the energy of the high-frequencywave and processes a substrate mounted on the stage in the vacuum vesselby using the plasma; said plasma-assisted processing system comprising:a lifting mechanism that moves the antenna vertically relative to thevacuum vessel; an electromagnetic shielding member surrounding a regionbetween the antenna and the high-frequency wave transmitting plate; alevel estimating unit that estimates a level of high-frequency wavecutoff density formed between the high-frequency wave transmitting plateand a plasma producing region; and a controller that controls thelifting mechanism to adjust the level of the antenna so that a cavity ofa proper size for the high-frequency wave is formed between the antennaand the level of a cutoff density for the high-frequency wave forproducing a plasma.
 2. The plasma-assisted processing system accordingto claim 1, wherein the level estimating unit includes: a transparentplate formed in a side wall of the vacuum vessel; and a cease regiondetecting unit optically detecting a lower limit level of a cease regionof a plasma produced between the high-frequency wave transmitting plateand a region in which the plasma is luminescent, and wherein a level forthe cutoff density is estimated on the basis of a detected lower limitlevel of the cease region for the plasma.
 3. The plasma-assistedprocessing system according to claim 1, wherein the level estimatingunit includes a high-frequency wave radiating unit that delivers adetecting high-frequency wave from above the plasma to the plasma, and ahigh-frequency wave receiving unit that receives the detectinghigh-frequency wave delivered and reflected by the plasma; wherein alevel of the cutoff density for the detecting high-frequency wave isdetermined on the basis of the position of the reflected high-frequencywave on the high-frequency wave receiving unit, and a level of thecutoff density for high-frequency wave producing the plasma is estimatedon the basis of the level of the cutoff density for the detectinghigh-frequency wave.